The present invention is directed to a method and apparatus for detecting and removing water from the surface of an object, and more particularly, it is directed to the use of radiant energy, for example infrared light, to detect and remove water from the surface of a moving metal sheet processed in a continuous treatment line to prevent the formation of water stains thereon.
Within the steel industry, many different types of steel strips are produced, often with various coatings ranging from other metals such as for example, tin, zinc, and zinc alloy, to organic protective layers. The different processing steps involved in manufacturing such a variety of different coated steel sheet products requires the strip to be uncoiled and recoiled many times. The uncoiled strip is often deliberately exposed to water or water containing components during the manufacturing process. If water accidentally remains on the strip when it is recoiled, the remaining water will cause various types of oxides to form within the coil windings, the formed oxides reducing product quality and sometimes ruining the entire steel sheet coil. Therefore, the presence of water must be avoided in coiled steel sheet product because the presence of water will lead to product loss at a considerable cost to the manufacturer.
FIG. 1, labeled Prior Art, shows the rinse section 1 of a typical continuous coating line. The steel sheet 3 is shown exiting a scrubber tank 5, moving through hot air dryers 1 and 13, and entering a coiler 7 where the steel sheet product is coiled for further processing or packaged for customer shipping. In a high speed coating line, the steel sheet product 3 travels at speeds of up to 3000 feet per minute. The fast moving sheet exits the scrubber tank 5, is sprayed with an oil/water emulsion at sprayer 9, and the strip passes through a set of wringer rollers 11 where excess water is xe2x80x9csqueezed offxe2x80x9d or removed from the product surface. To further insure that all water is removed from the steel sheet surface, the sheet product 3 passes between a plurality of hot air dryers 1 and 13 before reaching tension bridle rolls 7 of the coiler. At the higher speeds encountered in modem coating lines, the wringer rolls 11 are less effective at removing excess water from the product surface. As a result, there is a vary real possibility of having water present on the steel sheet surface when the strip 3 enters coiler (not shown).
State-of-the-art systems employed to remove the water occasionally fail to operate properly resulting in inferior product. Thus, it is desirable to have a system that automatically and non-invasively detects the presence of water on the moving steel sheet or strip 3, which heretofore has been void in the art. Previously, the only known method of detecting water was to manually hold a tissue or other water absorbent material on the surface of the steel sheet as it moved toward the coiler, and visually inspect the tissue for evidence of moisture. However, such a method is dangerous, inconsistent, and impractical.
It is known in the prior art to detect defects on a moving body such as a cold rolled strip. U.S. Pat. No. 3,734,628 discloses a method and apparatus for detecting defects in strip product, and the U.S. Pat. No. 3,734,628 is incorporated herein by reference. The ""628 reference teaches coating the strip with a film of oil, and the apparatus scans the surface with infrared light, having a specified wavelength range capable of penetrating the oil to detect underlying defects. However, such a method and apparatus for detecting defects is not suited for detecting the presence of water on a steel sheet surface moving at high speed.
U.S. Pat. No. 5,684,296 discloses using infrared light to detect the presence of a liquid, and the U.S. Pat. No. 5,684,296 is hereby incorporated herein by reference. However, this application is incompatible with the use of electronic sensors and requires the optical device to come into contact with the liquid. Therefore, the 296 patent does not have practical application as a non-invasive system for the detection of water, and in particular, for the detection of water on a continuous moving metal sheet.
Additional methods and apparatus to detect water in other environments are also known in the art. However, these prior art applications have no practical application for detecting water on a surface of an object as in the present invention.
Generic methods and apparatus to scan objects with infrared light or other light are well known in the art and are disclosed in various forms in the following references, U.S. Pat. Nos. 5,929,996; 5,835,220; 5,761,999; 4,005,926; and 3,825,351, all of which are incorporated herein by reference.
Therefore, as clearly illustrated above, there is a long felt need within the industry to provide a non-invasive method and apparatus for detecting the presence of water on a surface of an object, and particular, there is a long felt need to provide a method and apparatus capable of detecting the presence of water on the surface of a continuous steel sheet moving at a high speed in a manufacturing operation.
The present invention is directed to a method and apparatus for detecting the presence of water on a surface of an object using radiation. A surface area to be detected is illuminated with radiation having a wavelength substantially absorbed by water. An optical system is employed to view images reflected from the surface area. A bandpass filter is disposed between the surface area being monitored and the sensor to limit transmission of radiation to within a specific range of wavelengths known to be strongly absorbed by water. Thus, areas having no water will appear brightly illuminated and the reflected radiation more intense and areas where water is present will appear dark, the reflected radiation being less intense. The sensor assembly produces a signal representative of the intensity of the reflected radiation. If the intensity signal is lower than a predetermined level, water is detected and the signal may be used to trigger alarms or otherwise control the environment of the object. The present invention is particularly suited for detecting the presence of water on a moving strip of metal during a manufacturing process.